A 5.0 L sample of gas is collected at 400. mmHg at 727 C. What is the volume if the temperature were cooled to 77 C and the pressure increased to 700. mmHg?

u will equate and make V2 the subject because it's the one u are looking for ....

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.